The present invention relates to a magnetic ignition system for an internal combustion engine, especially a motor chainsaw. Such a magnetic ignition system has a magnet wheel that revolves with the crankshaft of the engine, at least one permanent magnet which rotates with the magnet wheel, and an armature with coil connected to the housing. A voltage is induced in the coil by the permanent magnet, the voltage being supplied to an energy storage. A magnet support is arranged at the magnet wheel for receiving the permanent magnet.
A magnetic ignition system of the aforementioned kind is known from German Patent 36 30 723. A magnet wheel revolving with the crankshaft has a permanent magnet at one section thereof which, at a certain angular position of the magnet wheel, is located opposite a U-shaped armature with coil. Due to the magnetic flux changes caused by the closing and opening of the magnetic circuit between permanent magnet and armature, a voltage is induced in the coil which is used to load a capacitor. At a defined ignition point, which may be derived from the induced voltage, the capacitor is discharged via the ignition coil that generates an ignition spark at a spark plug arranged within the combustion chamber.
The permanent magnet arranged on the magnet wheel is displaced by a small amount radially inwardly relative to the periphery of the magnet wheel and is provided with two pole shoes. The pole shoes are comprised of a magnetically conducting material and extend to the periphery of the magnet wheel so that the formation of a magnetic circuit between the permanent magnet and the armature is possible. In order to support the centrifugal forces generated upon rotation of the magnet wheel, the pole shoes and the permanent magnet must be secured in a suitable manner.
The magnet wheel, for a secure receiving and supporting of the pole shoes and of the permanent magnet, must be provided in a correspondingly stiff and heavy embodiment. This is disadvantageous with respect to the total weight of the combustion engine, especially for hand-held working tools such as, for example, motor chainsaws.
It is therefore an object of the present invention to improve a magnetic ignition system of the aforementioned kind such that for a lightweight construction of the magnet wheel and for a high magnetic flux the acting centrifugal forces can be securely supported.